OverviewIndonesia is the country with the most active volcanoes on Earth. There are around 130 active volcanoes and many more that are extinct. As such, Indonesia offers many opportunities for outdoor enthusiasts. There is an abundance of places to go for day hikes as well as many multi-day trip opportunities and relatively easy ascents of peaks up to 3800 meters. Given its many active volcanoes, there is at least one significant eruption somewhere in Indonesia every year, often more. Therefore, Indonesia is also a great place for the volcano watcher.
Volcanic Regions of IndonesiaRather than just grouping the volcanoes of Indonesia by the fault lines or geologic regions they belong to, we describe here the main volcanically active regions by the geography of large individual islands and groups of islands. For each region, we mention some of the most well-known or active volcanoes, although numerous others exist (see the map below for a somewhat more complete list).
The western side of the large island of Sumatra consists of a long mountain range that is lined with numerous volcanoes, many of them active. The more well-known of them include Sibayak near Medan in the North as well as Marapi, Talang, and Kerinci in central western Sumatra. Marapi and Kerinci are particularly active, and the latter is also the highest volcano of Indonesia and its tallest mountain outside of Papua. Also very active Anak Krakatau, child of the infamous Krakatau volcano that destroyed itself in a massive explosion in 1883, lies on its own island in the Sunda Strait between Java and Sumatra, and administratively belongs to the latter.
Java and Bali
The line of volcanoes spanning Sumatra continues across the Sunda Strait on Indonesia's most populous major island, Java. Most volcanoes on Java lie towards the southern coast, although such separation is less pronounced than on Sumatra. Major active and well-known volcanoes on Java include Gede-Pangrango, Papandayan, Slamet, Merapi, Bromo, Semeru, and Ijen. Bali, which is separated from Java only by a narrow strait to the east, hosts two more active volcanoes: Agung and Batur.
Nusa Tenggara translates to "Southeastern Islands" and refers to the chain of islands east of Bali, ranging from Lombok all the way to the Alor group of island. It can be seen as the continuation of the chain of volcanoes spanning Sumatra and Java. Major volcanoes in this region include Rinjani on Lombok, Tambora on Sumbawa, Ebulobo, Kelimutu, and Egon on Flores, and Ili Api on Lembata. Tambora was the site of the cataclysmic eruption of 1815, although the mountain is now completely quiet.
An entirely different and very active region of volcanoes lies at the northern top of Sulawesi island and stretches across the Sangihe group of islands towards the Philippines. Major active volcanoes here include Soputan, Lokon-Empung, Karangetang, and Awu.
Across the Maluku Sea from North Sulawesi lies Halmahera island of the northern Moluccas. Along with some smaller surrounding islands it hosts another set of regularly active volcanoes. Some of the more interesting are Gamalama, Gamkonora, Ibu, and Dukono.
The Banda Sea south of the Moluccas hosts another few volcanoes on small islands, the most well-known of them being Banda Api.
Volcanic ActivityAmong the several hundred volcanoes in Indonesia, many dozen are still active. Levels of activity range from a few eruptions per century to the continuous activity with up to several eruptions per hour of Semeru volcano. A typical year in Indonesia sees at least one significant eruption somewhere within the archipelago, and often more. For current activity levels, check the website of the Center for Volcanology & Geological Hazard Mitigation (see external links). The site is mostly in Indonesian, but brief descriptions of major volcanoes and updates on significant activity are given in English as well.
Hiking, Climbing, and CampingWhile there are some technical climbs in eastern Indonesia (Papua), none of the volcanoes are technically difficult. Furthermore, Indonesia's islands are all scattered around the equator and it takes a lot of elevation at those latitudes for snow to persist. With the highest (Kerinci in Sumatra) standing at 3805 meters, none of the volcanoes reach such height. As a result, most can be done by hiking and scrambling.
The terrain for the approaches can reach from well-used hiking trails with established camping spots to unrecognizable paths through thick and fast-growing jungle, in which case a guide and/or a machete could be essential. The actual climb is often through jungle and forest on the lower slopes and more open steep terrain on the upper slopes. For recently or frequently active volcanoes, the last part of the climb often involves scrambling over lose scree and ash. The approach and climb of lower-altitude summits can be a hot endeavor and the latter is usually done at night. Higher-altitude climbs can surprise the hiker accustomed to the tropical surroundings with freezing temperatures and strong chilly winds, especially at night.
Camping is common and easily possible on any route that requires more than a day. In some wilder and less-traveled places you can just camp wherever you want - "leave no trace" should be adhered to in either case, even if many local hikers do not always do so. With no snow around and the hot climate, water can be an issue. On some climbs water is available in small springs or streams, but there are also many regions of tropical rain forest that do not actually have any flowing water, in which case all water for the trip has to be carried along.
Climate and SeasonsBeing a tropical country, Indonesia only has two seasons - wet and dry. Temperatures are near-constant all year round. For most of Indonesia, the dry season, i.e. the most interesting season for outdoor trips, lasts roughly from June to September and the wet season from December to March. The periods in between are transitional. The dry season is perhaps most pronounced in Nusa Tenggara. Sumatra is quite wet year round, even during the "dry season". A big exception is the region of the Moluccas, which also includes the Banda Islands, where seasons are reversed. December through March are dry here, and June through September are wet.
External LinksVolcanoes of Indonesia, Global Volcanism Program of the Smithsonian Institution
Indonesia Volcanoes and Volcanics, US Geological Survey
Center for Volcanology & Geological Hazard Mitigation (some English)
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